Inorganic glass, a transparent material, has heretofore been used for panel substrates and the like in displays such as liquid crystal display devices and organic EL display devices. However, inorganic glass has higher specific gravity (heavier), as well as lower flexibility and impact resistance. In this situation, use of a polyimide film which is lightweight and excellent in impact resistance, workability and flexibility for a panel substrate of a display apparatus has been taken into consideration. For example, use of a polyimide film obtained by reacting bis(trifluoromethyl)benzidine with a tetracarboxylic dianhydride component for a substrate for a display apparatus has been proposed (PTL 1).
The panel substrate for a display apparatus requires high light transmittance. In a display apparatus, an image displayed by a device is observed through the panel substrate. Accordingly, the panel substrate also requires a small retardation in the traveling direction of light (thickness direction of the substrate). In addition, in a process for forming a device on a panel substrate, heat may be applied to the panel substrate. Therefore, the panel substrate also requires high heat resistance and high dimensional stability (coefficient of linear thermal expansion being small).